The present invention relates to a workpiece carrier for a polisher and more particularly to a carrier used for polishing both surfaces of a workpiece to be polished, such as semiconductor wafers typified by a silicon wafer and a gallium arsenide (GaAs) wafer, thin glass, ceramics, artificial quartz, metal sheets, and so forth.
Polishing of both surfaces of a semiconductor wafer has been carried out by use of a double-sided polisher, which is shown in FIGS. 10 and 11, in the following way. First of all, polishing sheets 12, 14 are bonded to each of the opposed surfaces of upper and lower stools 11, 13 of a double-sided polisher 10. A plurality of carriers C equipped around their outer periphery with teeth meshing with a sun gear 15 and an internal gear 16 of the double-sided polisher 10, are disposed in such a manner as to attain the engagement between the teeth and the gears. Then, the semiconductor wafer W to be polished is inserted into each workpiece insertion hole 3 bored in each carrier and clamped by the upper and lower stools 11, 13. Thereafter, the sun gear 15 and the internal gear 16 are rotated so as to cause the rotation and revolution of the carriers C while a polishing solution is being charged between the upper and lower stools 11, 13 and to cause spiral movement of the semiconductor wafer W between these stools. At the same time, the upper and lower stools 11, 13 are rotated so that the polishing sheets 12, 14 and the polishing surfaces of the semiconductor wafer W come into mutual rubbing contact and the latter is ground. The conventional double-sided polisher is disclosed in Japanese technical literature entitled "CHOU-SEIMITSU KENMA KYOMEN KAKO GIJUTSU" (Ultra-precision Polishing & Mirror Polishing Technique), pages 375-383, Keiei-Kaihatsu Center, Osaka, Japan 1987.
Since the thickness of the semiconductor wafers has become thinner and thinner in recent years, carriers having a smaller thickness have been sought. It has also been required recently to polish a large number of workpieces by a single carrier or to increase the diameter of the carrier. Almost all the conventional carriers are made of a glass fiber-reinforced plastic sheet or a blue steel sheet.
However, if a thin carrier is produced from a glass fiber-reinforced epoxy sheet, the accuracy of the thickness is low and its warp ratio is as high as from 2 to 3% so that the semiconductor wafer is likely to jump out from the workpiece insertion hole 3 and to get broken. Experiments have revealed an extreme difficulty in practice to reduce the warp ratio described above when a carrier was produced by a thin glass fiber-reinforced epoxy sheet.
On the other hand, the carrier made of a blue steel sheet is excellent in both the tooth strength and thickness accuracy but is not free from the same problems, in that when the thickness is small, it is likely that the warp of the sheet itself occurs, the workpiece jumps out and becomes broken, chipping occurs around the workpiece due to its collision against the carrier, and contamination due to metal ions may occur depending on the materials of the workpiece due to the direct contact of the workpiece with the metal surface.